Sewage treatment



J. R. DOWNES SEWAGE TREATMENT Filed Nov. 20, 1933 Cil Patented Dec. 22, 1936 UNITED STATES PATENT oFFicE sEwAGE TREATMENT John R. Downes, Middlesex, N. J., assigner to Pacific Flush-Tank Company, New York, N. Y., a corporation of Illinois Application November 20, 1933, Serial No. 698,734

' 9 Claims. (Cl. 210-2) This invention relates to an improved method of and apparatus for sewage treatment.

Its object is to provide a simple and inexpensive way of removing the suspended solids, and the vbiological oxygen demand from the sewage. More specifically, it relates to a new Way of introducing and using .chemicals in a treatment plant which includes a sprinkling lter or other biological oxidizing device or devices, whereby the capacity and eflciency of such a plant are increased. Ihis method also includes the return of some of the precipitated sludge to the incoming sewage and the use thereof with or without added chemicals in a primary settling tank to accelerate clarification and to deodorize the raw sewage.

other objects of the invention will appear in the following specication and the novel features thereof are set forth in appended claims.

In the art of sewage disposal, settling of the solids from the liquid at one or more points is standard practice. Plain settling or sedimentation is the common practice in nearly all sewage disposal plants. Chemical precipitation has been used from time to time in connection with sedi- 25 mentation but has not been satisfactory because of its high cost due to the large quantities of chemicals heretofore needed and to the 'large volume of sludge thereby produced.

sedimentation is used for clarifying the sewage for treatment in trickling filters or in other oxidation devices. Such installations have objectional features. Odors are liberated at the sprays. Filter ies, which breed in them are eliminated only by submerging the lter material periodically. The discharge of the flood water causes unloading of the chemical treatment so that complete and etecmay be secured with a minimum tive clarification dosage" of chemicals. Specifically, the organic combinations in raw or settled sewage. oier stubborn'resistance to the coagulating chemicals as ferrie or aluminum salts, which resistance is greatly reduced by a or the like. 33

lters and this unloadingv results in the temporary deterioration and/or.

prior treatment in such oxidizing devices. Furthermore, the chemical treatment of the efiiuent from the oxidizing devices completely removes the undesirable turbidity of such eiluents during the unloading periods following submergence as a means of y control, thus nullifying the bad temporary resuit of submerging the lters and assuring a plant eiliuent of the highest quality at all times.

I have also discovered that the sludge produced by chemical treatment of the emuent from trick- .ling lters or other oxidizing devices is an active `clarier of raw sewage and a good odor absorbing medium, and that such sludge, either alone or combined with additional doses of chemicals, is capable of reducing the organic load in the sewage applied tothe filters, beyond the limits which could be obtained by plain sedimentation and with much less chemical, than would be required without the return of sludge taken from the eiiluent from the filter or oxidizing device. 20

The drawing is a flow sheet or diagrammatic representation of an apparatus which embodies this invention and by means of which the novel method herein described may be carried out.

I0 designates a preliminary settling tank into 25 which sewage is introduced through a pipe |I. Sediment may be removed from the bottom of this tank through a valved pipe I2. I3 is a pipe which leads the eiiluent from tank l0 to a dosing tank from which it flows intermittently 30 through a pipe 2| to the jets 3| of a sprinkling filter 30. 32 is the lter filler of rocks, gravel is a pipe leading from the base of the sprinkling iter to a mixing tank 40. 34 is a valve in pipe 33. 4| vis a pipe from mixing 35 tank 40 to a secondary settling tank 50 from which the final eiliuent freel from suspended solids -is discharged through a pipe 5|.

'I'he apparatus shown is a standard arrangement with the exception of the interposition of 40 a mixingtank 40 between the sprinkling lter and the secondary settling tank 50. The sprinkling ilter is shown as an example of an oxidizing device.

The mixing tank comprises a compartment 42 45 a plurality of slow speed stirrers 48, and finally runs out through pipe 4l to the secondary settling tank 50.

Before describing -the other parts of the apparatus shown in the drawing, I will describe the operation of such of the i parts as have been pointed out specifically. The operation of clarifying sewage in the preliminary settling tank l0, leading it through a dosing tank 20 and oxidizing it in a sprinkling iilter 30 is the same as that heretofore used.

In treatment of sewage on a precipitation basis it is necessary to add enough of the coagulating chemical to raise the hydrogen-ion-concentration'v to a definite end-point. `Until this end-point is reached, the salt simply goes into solution, and again, beyond the specific end-point vit redis` solves. This end-point varies with different chemicals and with some coagulants any variation in either direction from the specific critical end-point is disastrous. It is an object of my invention to provide a means of eie'cting the desired precipitation with a minimum amount of chemicals under| conditions which can be controlled easily.

I have found that the oxidation of the settling tank eiiiuent removes about seventy-dive percent of the resistance of the sewage to the coagulating'eiect of chemicals so that the amount of chemicals required for complete clarification is greatly reduced by introducing the chemicals to the clarified sewage after it has been oxidized. With the former methods the amount of chemical required varies from time to time with vari'- ations in the character of the raw sewage, these variations, however, are eliminatedy by the passage of the sewage through an oxidizing device such as a sprinkling filter bed'.

I have also found that a savingl of chemicals is eiected by a violent and somewhat continued agitation of the sewage at the time the chemicals are added. The effect of the coagulant then becomes proportional tothe amount of coagulant introduced up to the critical end-point and the coagulant causes precipitation instead of going into solution. Thus the sewage is not rendered acid, no lime is needed to complete the reaction and a definite degree of clarification can be acomplished without producing an excessive volurne of sludge. In former chemical precipitation practice the volume of sludge is increased vthree hundred to four clariication of the sewage is procured. With violent initial agitation as'much as i'lfty percent clarication of the sewage (in terms of organic load) may be secured with only about ten percent increase in volume of sludge.

With the system herein described two hundred pounds of chemicals, per million gallons of sewage, will do the work for which as much as fourteen hundred pounds has been required by vformer methods.

It has been mentioned that the filler 32 of the sprinkling filter is a breeding place for filter flies. These are eliminated by closing valve 3l -and ooding the iilter. After suchsubmergence the liquid is withdrawn by opening valve 3l. In former installations this withdrawal causes a turbidity of the eilluent. With lmy arrangement this turbidity is eliminated by manipulating valve 46 and introducing a larger amount of chemicals to mixing tank l0 during the periods of with drawal.

Between thebottom of the secondary settling tank S0 and its valved .discharge pipe il is a hundred percent before any- .part of the secondary conduit 60 which leads through a variable pump 6l to a mixing tank 'l0 on the side of tank i0. Il is a valved pipe through'which chemicals can be introduced into the mixing tank 10.

By this arrangement the sludge from tank 50 is to be mixed with the sewage entering tank I0, through pipe Il. Here the sludge, which has been subjected to chemical treatment, becomes mixed'with the incoming raw sewage on which it acts as adeodorizer and accelerates clarification. Its effect may be increased by the addition of a desired amount of chemicals introduced through the pipe 1I. lIn the latter case, the returned sludge forms a nucleusv for the formation of floc.

By the use of this arrangement and method the volume of sewage which can be successfully treated in a given area is greatly increased. Complete removal of suspended solids or better and uniform clarification may be obtained at all times with great eiilciency and at low cost. The saving in cost of chemicals over former chemical precipitation methods is as high as seventy-five percent. As` the total amount of sludge produced by this chemical treatment is only about ten percent greater than would be the case if no chemicals were used, compared with the undesired increase of three hundred to four hundred percent in the volume of sludge obtained by former chemical precipitation methods, the cost of sludge disposal is thus greatly reduced.

What I claim `is:

1. The herein described method of treating settled from the mixture with added coagulating chemical, in the preliminary settling step.

3. Sewage disposal apparatus comprising a primary settling tank, a biological oxidizing device connected therewith. a mixing tank connected with the oxidizing device, means for introducing chemical material into said mixing tank, a secondary settling tank, a connection between the mixing tank and the secondary settling tank, and means for returning material from the lower part of the secondary settling tank to the upper part of the primary settling tank.

4. Sewage disposal apparatus comprising a primary settling tank, a biological oxidizing device connected therewith, a mixing tank connected with the oxidizing device, means forl introducing chemical material into said mixing tank, a secondary settling tank, a connection 4between the mixing tank and the secondary settling tank, means for returning material from the lower settling tank to the upper part of the primary settling tank, and means for introducing chemical material with said returned material into the preliminary settling tank.

5. Sewage disposal apparatus comprising a primary settling tank, a sprinkling filter connected therewith, a mixing tank, a connection between the filter and the mixing tank, means for introducing chemical material into the mixing tank, a'secondary settling tank, a. connection between the mixing tank and the secondary settling tank.`

v I '3,065,123 and means -for returning material from the lower` part o! the secondary settling tankto the upper part of the primary settling tank.

6. Sewage disposal apparatus comprising a primary settling tank, a sprinkling filter connected therewith, a mixing tank, a valved connection between the filter and the mixing tank. regulable,

means for introducing chemical'material into the -mixing tank, a secondary settling tankfa connection between the mixing tank and the secondary settling tank, and regulable means for returning material from the lower part oi' the secondary settling tank to the upper part of the primary settling tank. l

,7, Sewage disposal apparatus comprising a primary settling tank, a sprinkling lter connected therewith, a mixing tank, a valve connection between the lter and the mixing tank, regulable means for introducing chemical material into the mixing tankI a secondary settling tank, a conv 8. Sewage disposalapparatus comprising a. priy mary settling tank,'a biological oxidizing device connected therewith, an agitating compartment for receiving the sewage from the oxidizing device, means for introducing chemical material to ble means for introducing chemie said compartment, a stirrer in said compartment arranged to produce a violent agitation of the sewage and chemical materiale. second com.

partment for receiving the mixed sewage and chemical material, means in said second compartment for maintaining the sewage and chemical materialin their mixed condition, a secondary settling tank and a connection between said second compartment and the secondary settling tank.v

Y 9. Sewage disposal'apparatus comprising a primary settling tank, a biological oxidizing device connected therewith, a compartment for receiving the sewage from the oxidizing device, regulamaterial to said compartment, a stirrer in said compartment arranged to produce a violent agitation of the sewage and chemical material, a second compartment for receiving the mixed sewage and chemical material, means in said second compartment formaintaining the sewage and chemical material in their mixed condition, a secondary settling tank, a connection between said second compartment and the secondary settling tank, regulable means for returning material from the lower part of the secondary settling tank to the upper part of the primary settling tank, and means for introducing chemical material to the returned material.

JOHN R. DOWNES. 

